UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Part A: Precipitation hardening in a TI-CU alloy Part B: The structural and nagnetic Properties of.. Howe, Lawrence Martin 1956-01-31

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
831-UBC_1956_A7 H7 P8.pdf [ 2.37MB ]
Metadata
JSON: 831-1.0081196.json
JSON-LD: 831-1.0081196-ld.json
RDF/XML (Pretty): 831-1.0081196-rdf.xml
RDF/JSON: 831-1.0081196-rdf.json
Turtle: 831-1.0081196-turtle.txt
N-Triples: 831-1.0081196-rdf-ntriples.txt
Original Record: 831-1.0081196-source.json
Full Text
831-1.0081196-fulltext.txt
Citation
831-1.0081196.ris

Full Text

PART A: PRECIPITATION HARDENING IN A TI-CU ALLOY PART BJ THE STRUCTURAL AND MAGNETIC PROPERTIES OF SOME QUARTERNARY ALLOYS OF Mn^oAl xZn 2 o^ xC20 AND Mn^Ga^Zngo^CgQ by LAWRENCE MARTIN HOWE A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of MINING.AND METALLURGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE. Members of the Department of Mining and Metallurgy. THE UNIVERSITY OF BRITISH COLUMBIA August, 1956 ABSTRACT The decreasing solid solubility limit at the titanium- rich end of the titanium-copper constitutional diagram suggests the possi b i l i t y that titanium-rich alloys may be age-hardenable. However, results obtained by previous investigators, using lump samples, show that after quenching from 790°C the age-hardening of an alloy contain ing 1,7 percent copper is very light while a 0.8 percent copper alloy decreases in hardness, during heat treatment at 400°C, It was believed possible that powder samples of alloys might show different results from the lump samples used by previous investigators. Consequently, a 1.90 percent copper alloy was made by the technique of levitation melting, checked for homogeneity, and f i l i n g s of 48-65 Tyler screen size were cut from i t for aging experiments. Hardness readings do show a hardness peak at aging tempera tures of 400°C, 450°C, and 500°C and thus indicate that the titanium-copper alloy is susceptible to age-hardening treatments. Interest i n the MnDoAlxZn2o_x('20 a n d ^ 6 0 G ax Z n20-xC20 sy 8tems results from pregious studies of Mn-Al-C, Mn-Zn-C, and Mn-Ga-C systems; i n particular the alloys near compositions ^n^^A^o^o* M^O^^O^O' a n (* M n60Ga 20 c20» The saturation magnetization (cr) versus temperature (T) curve for alloys near the compositions MnkQA^QC^o a n c* Mn6oGa20^20 sh°ws normal ferromagnetic behaviour from 0°K to the Curie points of the alloys. Alloys near the composition Mn5oZn2oC20> o n t n e other hand, have abnormal behaviour as they experience a maximum i n thecr-T curve i n the neighbourhood of -40°C. Reasons for investigating the Mn6o^-^n20-x^20 6 1 1 1 ( 1 ^n60^ax^n20-x^20 systems were: 1. to provide further data regarding the presence of abnormal behaviour i n Mn^QZ^o^O a n d °^ n o r m a l behaviour i n Mn^ QALgo^ o and Mn6oGa2QC2o» (i.e. alloys near these compositions). 2. to suggest how the valency of the cube-corner atom affects the normal ferromagnetic moment of these alloys. However, investigation of these systems has lead to even more complicated phenomena, and the above two items remain, to a large extent, unsolved. ACKNOWLEDGEMENT The author is grateful for financial aid in the form of a research assistanceship provided by the Defence Research Board of Canada. The precipitation hardening studies in the Ti-Cu alloy were originally started by E. Saaremaa in parti a l fulfilment of B.A.Sc, requirements. This work is part of a program sponsored by the Defence Research Board of Canada, Project Number 7501-18. Funds for the magnetic studies were provided by the Defence Research Board under Research Grant 281. Assays were required for the Mn0oAlxZn2o_xC2o a n (* ^ n6oOaxZn2o_x^20 alloys and these were kindly done by the Cosma Testing Laboratories in Cleveland, Ohio. The author i s grateful for the assistance of the staff of the Department of Mining and Metallurgy. Special thanks are extended to Dr. J. Gordon Parr, director of the Ti-Cu research, Dr. H.P. Myers, director of the magnetic research, and R.G. Butters for technical advice and en couragement. TABLE OF.CONTENTS PART A: PRECIPITATION - HARDENING IN A TI-CU ALLOY Page I. INTRODUCTION . 1 II. PREVIOUS WORK 3 III. EXPERIMENTAL PROCEDURE 1. Preparation of the alloys 4 2. Heat treatments 5 3. Microhardness measurements 5 IV. RESULTS 7 V. DISCUSSION OF RESULTS AND CONCLUSIONS 9 VI. BIBLIOGRAPHY . . . . . 10 PART B: THE STRUCTURAL AND MAGNETIC PROPERTIES OF SOME QUATERNARY ALLOYS OF Mn6oAlxZn20-xC20 a n d M n 6 0 G ax Z n 2 0-x ° 2 0 I. INTRODUCTION 11 I I . PREVIOUS WORK 1. Mn-Al-C system 14 2. Mn-Zn-C system . . 15 3. Mn-Ga-C system 16 III. EXPERIMENTAL PROCEDURE 1. Preparation of alloys 19 2. Magnetic measurements 19 3. X-ray measurements and mircroscopic examination 20 IV. RESULTS 1. Mn6oAlxZn20-xC20 system 22 2. Mn6oGaxZn20-xc20 system 32 V. DISCUSSION OF RESULTS AND CONCLUSIONS . . 37 VI. BIBLIOGRAPHY 42 ILLUSTRATIONS PART A: Page 1. a s o l i d s o l u b i l i t y and e u t e c t o i d r e g i o n on the h i g h t i t a n i u m s i d e of t h e T i - C u phase diagram ( a f t e r Joukainen e t a l ) 2 2. E f f e c t o f 400°C a g i n g on hardness o f T i - C u a l l o y s (both i n lump form) s o l u t i o n annealed i n the a f i e l d as determined by Holden et a l 3 3. Photograph of a l e v i t a t i o n - m e l t i n g u n i t i n o p e r a t i o n . . . 6 4* Photograph of a t y p i c a l t i t a n i u m a l l o y i g n o t • 6 5. E f f e c t o f 4CO°C, 450°C, 500°C a g i n g on hardness of a 1.90$ Cu a l l o y , i n powder f o r m , as determined by the a u t h o r 8 PART B : 1, G e n e r a l r e l a t i o n between s a t u r a t i o n v a l u e and temperature f o r f e r r o m a g n e t i c s . . . . . . . 11 2, The p e r o v s k i t e s t r u c t u r e f o r Mn6c-Al2Q.C20> Mn6oGa2QC20» 3 1 1 0 1 ^ O ^ Z O 0 ^ 1 3 3. S a t u r a t i o n m a g n e t i z a t i o n versus temperature f o r a l l o y s near the composi t ions Mn£,oAl2oC20» M n60 G a20 c20* M n 6 0 Z n20 C20 ^ 4. V a r i a t i o n of s a t u r a t i o n m a g n e t i z a t i o n w i t h temperature f o r h i g h z i n c content a l l o y s i n the Mn5QAlxZn2o_x^20 system 25 5. V a r i a t i o n of s a t u r a t i o n m a g n e t i z a t i o n w i t h temperature f o r h i g h aluminum content a l l o y s i n the Mn6oAlxZn20-x^20 system 26 6, V a r i a t i o n o f s a t u r a t i o n m a g n e t i z a t i o n at 0°K w i t h atomic p e r  cent aluminum f o r the Mn^oAl x Zn 2 o- xC20 system 27 ILLUSTRATIONS (continued) Page 7« Bohr magneton value versus atomic percent aluminum for the Mn6oAl xZn20-x^20 system . . . . . 28 8. Variation of Curie temperature with atomic percent aluminum in the Mn5QAl x Zn2o_ x ^20 system 29 9, Variation of lattice parameter with atomic percent aluminum for the MnoQAlxZn20-x c20 system 30 10. Comparison of X-ray intensity plots at -186°C and 20°C for a 2.85$ Al alloy 31 11. Variation of saturation magnetization with temperature for alloys in the Mn5oGa x Zn20- x ^20 system . o . . . . . . . 33 12. Variation of saturation magnetization with atomic percent gallium for alloys in the Mn 0 o G ax Z n 20-x^20 s y s t e m 4^ 13. Bohr magneton value versus atomic percent gallium for the Mn£,0GaxZn2o_xC2o system 35 14. Variation of lattice parameter with atomic percent gallium for the ^6o G ax Z n 20-x^20 system 36 15. Variation of Bohr magneton value with lattice parameter for Mn 6 0Al 2 0 C 2 0 , ^ H c^oCgo, and Mn^oZr^^o , 39 PART A: PRECIPITATION HARDENING IN A TI-CU ALLOY I. INTRODUCTION The necessary condition for carrying out a precipitation hardening process on an alloy i s that at room temperature there shall be present in the slowly cooled alloy a large amount of one phase and a smaller amount of a second phase. The f i r s t constituent must be capable of dissolving a l l or an appreciable amount of the second constituent as the temperature is raised. The decreasing solid s o l u b i l i t y limit at the titanium-rich end of the titanium-copper constitutional diagram"*" (Figure l ) suggests the possibility that titanium-rich alloys may be age-hardenable. Re ferring to Figure 1, we see that at 79&°C, copper is soluble i n titanium to the extent of 2 ,1 percent, whereas the so l u b i l i t y i s approximately 0.5 percent at room temperature. Ordinarily, concentrations of the hardening constituent approaching maximum solid s o l u b i l i t y in the a phase at the eutectoid temperature are chosen. The f i r s t step i n the heat treatment is to heat the alloy to a temperature i n the a phase f i e l d i n order to obtain a solid solution of uniform composition. The saturated solution thus formed is quenched or at least cooled at too rapid a rate to permit the separation of the second phase that would normally occur with slow cooling. As a result of the rapid cooling, the alloy i s in a state of supsrsaturation and i s therefore thermodynamically unstable. The subse quent age-hardening of the alloy is a result of the decomposition of the solution, which in some alloys occurs at ordinary room temperatures but usually requires a relatively low temperature heat treatment. - 2 - 500 l.<J©% 2 3 4 5 6 7 8 Weight Percent Copper 10 Fifrure 1 a solid solubility and cutectoid region on the high titanium side of the Ti-Cu phase diagram. - 3 - II PREVIOUS WORK 2 Results obtained by Holden et a l reproduced i n Figure 2 show that after quenching from 790°C the age-hardening of an alloy containing 1.7 percent copper i s very slight, while a 0.8 percent alloy decreases in hardness, during heat treatment at 400°C. However Holden et a l used lump samples and i t was believed possible that powder samples of alloys might show different results from the lump samples. Reason for believing thusly i s that small particles are often more sensitive to diffusion processes than larger samples. 150 Aging time i n Hours Figure 2 Effect of 400°C aging on hardness of Ti-Cu alloys solution annealed in the a f i e l d as determined by Holden, Watts, Ogden, and Jaffee. - 4 - III. EXPERIMENTAL PROCEDURE Preparation of the Alloys. Owing to the high melting-point of titanium (1800°C) d i f f i  culties are encountered i n melting techniques. Method adapted was that 3 of melting the titanium alloy by levitation in a high-frequency f i e l d . I n i t i a l preparation involved placing the required amount of copper (1.90 percent by weight) in a hole d r i l l e d i n a cylindrical iodide titanium sample. Weight of the prepared specimen was approximately 6 grams. The titanium-copper specimen was melted in about 30 seconds - and i t remained levitated, without dripping, in the molten state i n an argon atmosphere (Figure 3). When the c o i l current is switched off the metal drops into a copper mold directly below the c o i l . A typical ingot i s shown in Figure 4. .. There was no trace of reaction or sintering between the mold and the alloy. The ingots were shown to be homogenows both by micros - scopic examination and by the identical X-ray diffraction patterns which were obtained from similarly treated samples of different parts of the same ingot. Previous investigators i n the department had done checks on contamination. A piece of pure iodide titanium was melted, cast, and hardness readings were taken. The readings varied from R F 80 at the center to 90 at the outside, (usual hardness value quoted for pure as- cast titanium i s 70 to 75 Rp )• The ingot was melted a second and a third time and there was no change in these hardness values. Therefore, according to accepted standards, there was no contamination during melting. - 5 - • Heat Treatments. A gas-quenching furnace was used for quenching operations. Filings of 48-65 Tyler screen size were cut from the ingot and placed i n a small molybdenum boat. The boat and the sample were than placed i n a furnace, held i n an atmosphere of argon while heated to 790°C for several minutes, and then blown out of the heating zone into a flask by a jet of helium gas. No reaction occurred between the f i l i n g s and the boat and the f i l i n g s did not appear to be sintered. For aging, the f i l i n g s were sealed in vacuo in s i l i c a tubes and aged at temperatures of 400°C, 4509C, and 500°C for various time intervals. Microhardness Measurements. Hardness readings were taken on a Bergsman Microhardness Tester, using a 25 gram load applied to a diamond indenter. Filings were mounted in lucite for this test. Figure 4 Photograph of typical titanium alloy ingot. - 7 - IV. RESULTS Hardness readings taken at various time intervals for aging temperatures of 400°C, 450°C, and 500°C are plotted in Figure 5. From this graph i t is seen that a hardness peak is obtained at each aging temperature. About a dozen readings were taken on each heat-treatment sample; the highest reading and the lowest reading were ignored and an average taken of the remaining values. In Figure 5 the curves pass through the average readings while the extent of scatter i s shown by the length of the vertical lines drawn through each point on the curves. Micro-structures of a l l samples were examined and X-ray gonio meter plots were taken between 20 values of 34° and 44° for as quenched, age-hardened 10 minutes, and age-hardened 1000 minutes samples for a l l three aging temperatures. Microstructures showed the presence of a only and likewise Xrray goniometer plots only revealed the presence of close- packed hexagonal a lines namely: 100 at 35°, 002 at 38.2°, and 101 at 40.1°. No lines at 39*5° and 43° characteristic of T i 2 Cu were present, (above angles are 26 values). Aging Time i n Minutes Figure 5 Effect of 400°C, 450°C, 500°C aging on hardness of 1.90$Cu alloy, i n powder form, as determined by author. - 9 - V. DISCUSSION OF RESULTS AND CONCLUSIONS Microscopic and X-ray examinations failed to reveal any structural changes during the aging process. This is not too surprising since early stages of precipitation do not usually manifest themselves in ways that are readily detectable by metallographic methods and the extent of precipitation on overaging a 1.90 percent copper alloy is very small. It is generally accepted that during aging some hardening occurs as a result of stresses set up by 'pre-precipitation* processes. At low temperatures of aging actual precipitation never occurs and hence the hardness curve is asymptotic to a line parallel to the time axis. At higher temperatures of aging precipitation occurs, stresses are relieved, and the hardness curves f a l l off. In the titanium-copper alloy at temperatures between 400°C and 500°C the hardness curves show characteristics that are typical of overaging. Experiments conducted at lower temperatures by other investi gators, also using powdered samples, gave no positive indication of hard ness increase. Therefore, i t appears that the coherency between the pre cipitate and the matrix material is short lived at the temperatures investigated - a fact which may be peculiar to the titanium-copper system or to the use of samples of very small dimensions. Quite apart from this 'overaging* preculiarity, the results indicate that the titanium-copper specimens are readily susceptible to age hardening treatments. +This is in contrast with the behaviour of lump 2 samples which are reported by other workers to respond negligibly. - 10 - VI. BIBLIOGRAPHY 1. A Joukainen, N.J. Grant, C F . Floe, Trans A.I.M.E. (1952), 194, 766. 2. F.C. Holden, A.A. Watts, H.R. Ogden, R.I. Jaffee, Trans A.I.M.E. (1955), 203, 117. 3. D.H. Polonis, R.G. Butters, J.G. Parr, Research (1954), 7, 10s. 4. D.H. Polonis, J.G. Parr, Trans A.I.M.E. (1954), 200, 1148. - 11 - PART B: THE STRUCTURAL AND MAGNETIC PROPERTIES OF SOME QUATERNARY ALLOYS OF Mn6oAlxZn2o_xG20ANI1 Mn60GaxZn20-xC20 I. INTRODUCTION Weiss 1, i n his molecular f i e l d approach to magnetism, obtains the following relationship for ferromagnetics: <S/CG= tanh C«se/fl-0T) Where a i s the saturation magnetization at temperature in question, o© i s the saturation magnetization at absolute zero, T i s the temperature, and 0 i s the Curie point defined by: Where JX is the atomic or molecular magnetic moment, K i s Boltzmann's universal gas constant, and N i s the Weiss intermolecular f i e l d constant. In the above, Weiss i s using the assumption of quantum theory namely that there are only two directions permissible for the spins of the elections i e : parallel and antiparallel. The general relationship between saturation magnetization and 1.0 I 0 0 Figure 1 General relation between saturation value and temperature for ferromagnetics. - 12 - temperature which i s l i s t e d above i s p l o t t e d i n F i g u r e 1. The e x p e r i m e n t a l l y observed s a t u r a t i o n value of the f e r r o  magnetics does i n f a c t f a l l w i t h r i s i n g temperature reaching s u b s t a n i t a l l y zero at a temperature known as the C u r i e temperature o r magnetic change p o i n t . The observed r e l a t i o n s f o r the elements i r o n , c o b a l t , and n i c k e l are i n good agreement w i t h the above t h e o r y . A p l o t o f s a t u r a t i o n value (<Jl) versus temperature (T) f o r a l l o y s near the compositions HnDQAl2QC2Q a n d ^n60Ga20^20 i n d i c a t e t h a t these a l l o y s obey normal ferromagnetic behaviour from absolute zero t o the C u r i e p o i n t s . However, a l l o y s near the composition MnDQZn2oC20 do not e x h i b i t normal ferromagnetic behaviour as a maximum occurs i n the C" - T curve at approximately -40°C. In order to o b t a i n f u r t h e r i n f o r m a t i o n w i t h regard to t h i s abnormal behaviour , i t was desirfjable to i n v e s t i g a t e the magnetic p r o  p e r t i e s of the systems Mn 0oAl x Zn 2 Q_ x C2o a n d M^oG^xZr^O-xC^O* A l l o y s o f the compositions Mn 0QAl 2oC2o> Mn6oOa20^20 a n d 6^02^ 20^ 20 have a h i g h l y - o r d e r e d s t r u c t u r e i n which manganese occupies f a c e - c e n t e r p o s i t i o n s of cube, carbon occupies the body-center p o s i t i o n , and aluminum, g a l l i u m , or z i n c atoms are a t the cube c o r n e r s . The proposed s t r u c t u r e appears i n F i g u r e 2. Through an i n v e s t i g a t i o n of Mn0oAlxZn2o_xC2o a n d Mn60GaxZn20-x<'20 systems, i t was thus a l s o d e s i r e d t h a t i n f o r m a t i o n couM be obtained which would suggest how the valency of the cube-corner atom a f f e c t s the normal ferromagnetic moment of these a l l o y s . - 13 - Figure 2 The proposed structure of Mno0Al2oC20> M n60 G a20 c20» a n d Mn60Zn20C20« - 14 - II. PREVIOUS WORK Mn-Al-C System 2 Butters and Myers investigated alloys close to the composition ^ n 6 o A l 2 0 G 2 0 > For a fixed carbon content of 20 atomic percent the single face-centered cubic structure occurs over the composition range Mn 60-69 atomic percent (hence Al 2 0 - 1 1 atomic percent). Increasing the manganese content beyond 60 atomic percent to 70 atomic percent causes an increase i n the Curie temperature from 0°C to 300°C, a decrease in the saturation magnetization from 1 .20 to approximately 0.6 Bohr magnetons per manganese atom, and a slight increase i n the lattice paramater from 3.869A0 to 3.874A0. This decrease in magnetization as the manganese content i s increased past 60 atomic percent can be explained by assuming that the magnetization of the additional manganese atoms, which must replace aluminum atoms in cube corner positions, i s antiparallel to that of those in the face-centered positions. The magnitude of the decrease i n magnetization corresponds to the extra manganese atoms having an effective Bohr magneton value of -4. In these alloys the saturation magnetization below the Curie temperature varies with temperature in a normal ferromagnetic manner as can be seen i n Figure 3 for an alloy near the composition Mn0oAl2oC20* Paramagnetic behaviour above the Curie point seems to indicate ferrimagnetisra, however neutron diffraction results indicate that Mn6oAl2oQ20^-s ferro magnetic. - 15 - Mn-Zn-C System Butters and Myers-' also investigated the behaviour of alloys near the composition Mn^QZ^gC^O' w i t n i n t n e range of composition studied, C 20 atomic percent, Zn 10-20 atomic percent, Mn 70-60 atomic percent, i t was found that the structure of the alloys was face-centered cubic. In creasing the manganese content beyond 60 atomic percent to 70 atomic percent causes an increase i n the Curie point from 80° to 488°C and a decrease of the la t t i c e parameter from 3.925A° to 3.899A0. For alloys with a zinc content above 15 atomic percent a marked maximum in the magnetization occurs in the, region of -40°C to -50°C. Above this temperature the magnetization decreases i n the usual fashion becoming zero at the Curie point. Below this temperature region the magnetization decreases but the decrease becomes less the lower the temperature. This abnormal behaviour for an alloy near composition MnQ Zn2oC2o ^ s shown in Figure 3 . Also, for this alloy, i t was found that at -186°C the original face-centered cubic structure observed at room temperatures is slightly distorted becoming face-centered tetragonal with a=3.921A° and c/a=0.9947. Neel has shown that the magnetization of a ferrimagnetic sub stance may vary with temperature i n a similar manner to the abnormal be^ haviour observed i n above Mn-Zn^ -C alloys. Paramagnetic behaviour above the Curie point also appears to agree with that predicted by Neel for ferrimagnetics. However, results obtained by Dr. B. Brockhouse at Chalk River, using neutron diffraction techniques, seem to suggest a different magnetic concept. The concept proposed is that of opposing sublattices having different Curie points (the sublattices of a ferrimagnetic substance have the same Curie points). - 16 - The Curie point of one sublattice i s assumed to be -40°C, where the maximum in the saturation magnetization of Mn0QZn2oC20 occurs. The other Curie point is at 100°C as observed by magnetic measurements. The resultant magnetization i s a vector sum of the opposing sublattices. It i s also rather interesting to note that a second order specific heat anomaly corresponding to the Curie point of one sublattice- should occur at -40°C. Such an anomaly has been found to exist i n measure ments on Mn^ QGa2QC2o ^ y M. Swanson, here at the department. Mn-Ga-C System Butters and Myers started this study and the project was then continued by the author. X-ray Debeye-Bcherrer diffraction photographs show that, within range of composition, C 20 atomic percent, Mn 62-70 atomic percent, Ga 10-18 atomic percent, the alloys have a face-centered cubic structure. It was not possible to obtain an alloy of composition Mn£,oGa2oC20 a s made up alloys of this composition contained free carbon. Saturation magnetization variation with temperature for alloys indicated normal ferromagnetic behaviour such as that illustrated i n Figure 3 for an 18 atomic percent gallium alloy. The lattice parameter increases with increasing manganese content from 3.876A0 at 62 atomic percent manganes to 3.881A0, whereas the Bohr magneton value per manganese atom decreases from a value of 1.27 at 62 atomic percent manganese to 0.62 at 70 atomic percent manganese. This would seem to suggest that the additional manganese atoms (in excess of 60 atomic percent) are replacing the gallium atoms at the cube corners and the magnetization of the cube corner manganese atoms - 17 - i s antiparallel to that of those in face-centered positions. The magnitude of the decrease corresponds to a value of -4 Bohr magnetons for the extra manganese atoms„ - 18 - 100 200 300 400 Temperature °K F i g u r e 3 Saturation magnetization versus temperature for alloys near the compositions MnDoAl2()C20» ^ n60(Ja20p20> and Mn6oZn2oC20• - 19 - III. EXPERIMENTAL PROCEDURE Preparation of Alloys The materials used in the preparation of the alloys for this work were manganese of 99 .9 percent purity, zinc of 99.99 percent purity, aluminum of 99.99 percent purity, gallium of 99.99 percent purity and graphite of spectroscopic grade0 The f i r s t step i n the preparation of the alloys was to make Mn-Al-C and Mn-Ga-C master alloys. Melting was carried out by the process of induction heating under an atomosphere of argon after i n i t i a l evacuation and degassing. Melts were c h i l l cast under argon into a s p l i t brass mold. Ingots were annealed in vacua i n quartz tubes to remove coring and promote homogeneity. Zinc could not be included i n this melting stage due to i t s low d i s t i l l a t i o n temperature. Master alloys were then crushed and mixed with the appropriate amount of zinc f i l i n g s to produce the mixture for sintering. The mixture of powders was placed i n a clean fused quartz tube, the tube was evacuated and sealed, and the sintering was achieved by heating to 600°C for approxi mately one week. In some cases the alloys were recrushed and resintered. The sinters wer homogeneous but tended to decompose i f l e f t i n moist air for long periods. They were therefore kept i n a dessicator when not in use. Magnetic Measurements For the magnetic measurements- an external f i e l d of 16,200 oersteds was used. The f i e l d was obtained by means of an electromagnet having i t s poles shaped so that a uniform f i e l d gradient was produced over a volume considerably greater than that of the specimen. - 20 - A Sucksmith ring balance was used to measure the magnetization. The principal involves the comparison of the forces exerted in turn on a sample of alloy and a sample of iron under identical conditions. The magnetic properties of pure iron being accurately known, those of the alloy sample may be calculated. The alloy specimen experiences a force F x given by: whereCis the saturation magnetization,m i s the mass, and &\\/A-x is the f i e l d gradient. Under identical conditions an iron standard experiences a force: F. = 0-srt\, <JH/<ix The forces F x and F s are balanced by the restoring force of a beryllium copper ring and the displacement of the specimen i s measured by a displaced light beam passing through two mirrors attached to the ring. We thus obtain: K<J»= F x= 6-*n>xoH/dx from which: About 30-40 mg. of sintered alloy was used for measurement, this being placed in a platinum-iridium container. A furnace and dewar attachments permitted measurements over temperature range required namely between -190°C and Curie points (highest about 230°C). Paramagnetic measurements were not made as there would have been trouble arising due to the d i s t i l l i n g out of zinc at elevated temperatures. X-ray Measurements and Microscopic Examination Debeye-Sherrer powder photographs were taken and the lattice paramaters were calculated from these in the usual way. Low temperature X^ray intensity plots were made on alloys of high zinc content in - 21 - Mn^QAlxZn2o_xC20 system using a Geiger counter spectrometer. Samples were mounted in lucite, polished, etched with 4 percent n i t o l solution, and observed under the microscope. This examination served as an additional check as to whether the alloys were single phase or not. - 22 - IV. RESULTS MnAnAlyZn?o.vC2o System In Figures 4 and 5 the variation of saturation magnetization (o~) with temperature (^ ) j_ s shown for single phase alloys. Normal ferromagnetic behaviour is experienced by single phase alloys of aluminum content of approximately 5.5 atomic percent and up. Alloys with lower aluminum contents than 5.5 atomic percent have a maximum or very f l a t portion i n their saturation magnetization curves. An alloy consisting of 9.6 atomic percent aluminum was also studied and was found to have normal ferromagnetic behaviour but is not included on the graphs for sake of clarity. The point at which deviation from normal ferromagnetic be haviour occurs shall be referred to as the transition point, transition temperature or simply transition. The transition temperatures for 0, 2.85, and 4.6 atomic percent aluminum alloys are 231-2, 210±5, and 120±10°K respectively. In Figure 6 the saturation magnetization at 0°K (cs) is plotted against atomic percent aluminum. Normal ferromagnetic alloys are repre sented by only one point namely -ordinary which was obtained by an extra polation of the 0*-T curve. Alloys which do not have normal ferromagnetic behaviour are represented by two points namely 61 -ordinary and fii-extra ordinary. The f i r s t of these represents an extrapolation of the tf"-Tcurve (to absolute zero) above the transition temperature i.e. region characteristic of a normal ferromagnetic. C70extra-orindary represents an extrapolation of the CT-T curve below the transition temperature. Vertical and horizontal - 23 - lines through the points represent the deviations to be expected in the <r-T extrapolations and in the aluminum compositions. Single phase alloys were not obtainable between 10 and 16 atomic percent aluminum and the dotted line represent form of curve expected i f they were obtainable. The Bohr magneton values have been calculated and then plotted versus atomic percent aluminum. Even though deviations are not shown i t is to be understood that they are s t i l l applicable. Curve is shown in Figure 7. Curie temperatures were obtained from cr* versus T curves and are plotted versus aluminum content i n Figure 8. The variation of Curie temperature with composition certainly is of a rather complex form and since probably very l i t t l e i s to be gained from a study of same i t shall not be discussed further. X-ray Debeye-Sherrer powder photographs show lines characteristic of a face-centered cubic and also superlattice lines. Lattice parameters for single phase alloys decrease linearly from Mn0oZn2oC20 *° ^ "60^ 1-20^ 20 as can be seen from Figure 9. Dotted region of curve is that in which single phase alloys were not obtainable. X-ray line intensity plots were obtained at -186°C and 20°C for alloys of 2.85, 5.5, and 7.5 atomic percent aluminum. Photographs of re sults for a 2.85 percent alloy are shown i n Figure 10. From an examination of the photographs i t is noted that there is a definite broadening of 220 and 311 lines at -186°C whereas the 111 line remains unchanged. It appears that 220 and 311 lines are s p l i t t i n g into two components at -186°C but this i s not too well resolved. Results for the 5.5 and 7.5 percent alloys are not displayed but i t was found that the intensity plots gave no indi  cation of sp l i t t i n g or broadening of lines occurring. -2k- Let us consider for a moment the transition from a cubic to a tetragonal structure. Upon examination of the structures in question i t can be seen that as a structure changes from cubic to tetragonal one expects no sp l i t t i n g of X-ray lines for 111 and 222 planes. On the other hand one expects splitting of lines for 200, 220, 311, and 400 planes into two components with multiplicity factors of 2:1. - 25 - 1 0 0 9 0 T3 CD » 80 M «> o 01 ttO O c o •H -P cfl N •H -P (1) C a o •H -P nS f-. -P al CO 7 0 6 0 5 0 4 0 30 2 0 1 0 1 0 0 2 0 0 ' 3 0 0 Temperature °K 4 0 0 5 0 0 Figure 4 Variation of saturation magnetization with temperature for high zinc content alloys in the Mn^Al Zn 2 system. - 26 - Figure 5 Variation of saturation magnetization with temperature for high aluminum content alloys in the M n 6 0 A 1 x Z n 2 0 - x C 2 0 s v s t e m ' - 27 - 50 [ _j | j i i i i i i 2 4 6 8 10 12 14 16 18 20 Atomic Percent Aluminum Figure 6 Variation of saturation magnetization at 0°K with atomic percent aluminum for the M N 6 0 A 1x Z N 2 0-x C 2 0 sys t em. - 28 - o ordinary pa 0..8 _ 0.7 - 0.6 - 0.5 1 I l I l I i l I i 2 4 6 8 10 12 14 16 18 Atomic Percent Aluminum Figure 7/ Bohr magneton value versus atomic percent aluminum for the MhD()AlxZn20-x^20 sy 3^* 1 1 1' - 29 - Atomic Percent Aluminum Figure 8 Variation of Curie temperature with atomic percent aluminum i n the Mn 6 0Al xZn 2 0_ xC 2 0 system. - 30 - 3.950 _ 3- 850 I l i i i i i • i i 2 4 6 8 10 12 14 16 18 20 Atomic Percent Aluminum Figure 9 The variation of lattice parameter with atomic percent aluminum for the Mn^QAl^Z^o-x^O system. - 31 - Figure 10 Comparison of I-ray intensity plots at -186°C and 20°C for a 2.85$ Al alloy. - 32 - MnooGa^nao-x^O System The variation of saturation magnetization with temperature for single phase alloys i s shown in Figure 11 8 Alloys with gallium content greater than 6.63 atomic percent, which would be expected to show normal ferromagnetic behaviour, by analogy with Mn6oA^x Z n20-x^20 system, are not single phase unfortunately and hence cannot be considered,, Alloys with gallium contents less than 6.63 atomic percent experience the same magnetic phenomena as i n the aluminum system. Saturation magnetization versus atomic percent gallium and Bohr magneton values versus atomic percent gallium were plotted and appear i n Figures 12 and 13 respectively. The same interpretation of these graphs applies as that outlined i n the Mn6oAlxZn2o=xC20 section. Transition temperatures for alloys of 0,1.87 , and 3.79 atomic percent gallium are 231^2, 210±5, 185*5°K respectively. Curie temperatures were obtained from o^vs. T plots. Values obtained are 415-5°K for 1.87 percent gallium 390i5°K for 3.79 percent gallium 380±5°K for 6.63 percent gallium. Expected value for Mn^QZ^c^o i s 353-5 °K (no value obtainable for Mn6oGa2C)C2o) • ^ n e v a l u e s were not plotted as i t is f e l t that i t would be of l i t t l e use ..since no simple re lationship appears to exist between composition and Curie temperature for these alloys just as for the alloys i n the aluminum system. Single phase alloys exist only up to gallium concentration of 6.63 atomic percent. In this region X-ray Debeye-Sherrer powder photographs show lines characteristic of a face-centered cubic and also superlattice lines. Lattice parameters for these single phase alloys are plotted versus gallium content i n Figure 14. Beyond 6.63 percent gallium another face-centered cubic phase appears along with the original face-centered cubic phase. The f i r s t or original phase disappears with even higher gallium contents and i s replaced by a phase of unknown crystal structure which coexists with the second face- centered cubic phase. - 33 - Figure 11 Variation of saturation magnetization with temperature for alloys i n the Mh£)oGaxZn2o_x('20 system. -3k- 50 1 I I I I I I 1 1 —I 2 4 6 8 10 12 14 16 IB 20 Atomic Percent Gallium' Figure.. 12 Variation of saturation magnetization with atomic percent gallium for alloys i n the Mn£j0GaxZn2o_xC2o system. - 35 - O Ordinary ^ 0 Extra-ordinary OQ _L 8 10 12 14 Atomic Percent Gallium 16 18 20 Figure 13 Bohr magneton value versus atomic percent gallium for the Mn6oGax^n20-x^20 system. - 36 - Atomic Percent Gallium Figure 14 Variation of lattice parameter with atomic percent gallium for the M L60 G ax Z N20-x C20 S T S T E M * - 37 - V. DISCUSSION OF RESULTS AND CONCLUSIONS The assay results indicated that i t was rather d i f f i c u l t to obtain alloys, i n the M n6oAL x Z n20-x G20 a n d l f o60 G ax2 n20-x^20 systems, by sintering process, which had compositions same as those originally desired. However i n most cases the f i n a l percentages of constituents were f a i r l y close to the as-made-up compositions and i n those cases where they were not the alloys were discarded. In order to make plotting of graphs and interpretation of results easier percentages of zinc and aluminum in Mn^QAlxZn2o_xG20 system were adjusted so that the aluminum plus zinc atomic percents totalled twenty, similarly for the gallium and zinc i n the Mn5oGaxZn2o»xG20 system. ' Manganese and carbon percentages may be considered as being essentially 60 and 20 atomic percent respectively as the assay results indicated that i n most cases they were within one atomic percent of these figures. Variation to be expected i n composition has been shown on graphs or accounted for i n some manner and i t i s important to note that even though there i s this slight variation i n composition that the general trends as indicated i n the graphs are unquestionably reliable. Single phase alloys obtained i n the Mn0oAlxZn20-xG20 a n d ^60 G ax Z n20-x^20 s y s t e m s were found to be highly-ordered structures as shown by Debeye-Sherrer powder photographs and inferred from structure determination for alloys close to the compositions Mn^QA^e-Cao a n d M n60 Z n20 c20'' 1 x 1 t h i s highly-ordered structure manganese occupies face-center positions of cube, carbon occupies the body-center position, and aluminum, gallium or zinc atoms are at the cube corners. It i s unfortunate that single phase alloys - 38 - could not be obtained over the complete range, of compositions i n the two systems. Bohr magneton values expected for MnooA^Q^O a n d M n60 Z n20G20 a r e 1.23 and 1.58 per manganese atom respectively. Since there are three manganese atoms per unit c e l l this would correspond to 3.69 and 4.74 Bohr magnetons per unit c e l l of Mn0oAl2oC20 a n d Mn60Zn20G20° ^he difference between the two values ±6 of the order of 1 $ohr magneton and the difference between the valency of aluminum and zinc, which are corner atone, i s one. This would seem to suggest that the moment of the unit c e l l of this type of alloy i s governed by the valency of the atom at the corner s i t e . Hence we might expect the magnetic moment to decrease linearly as we go from Mn60Zn20c20 *° Mn60Al20C20« Consider now the Bohr magneton value expected for Mn6QCa20G20 namely 1.43 Bohr magnetons per manganese atom or 4.29 Bohr magnetons per unit c e l l . Gallium has the same number of valence electrons as aluminum yet we obtain a different magnetic moment. Ppssible explanations of same are: 1. different interatomic distances 2. difference i n t o t a l number of electrons. Also i f valency of the cube corner atom were governing factor we would once more expect a linear decrease i n the magnetic moment as we go from Mh60Zn20C20 t 0 Mn60c,»20C20 • The difference i n interatomic distances i n above alloy systems does not appear to be a governing factor as far as magnetic moment i s con cerned. Consider for example the plot of the expected parameter versus the expected Bohr mangeton value for Mn0QAl2oC20> ^ n60Zn20G20 a n d ^ 60^*20^20 as illustrated i n Figure 15. If the parameter was a governing factor one would.expect a linear relationship between the paramater and the Bohr ~ 39 - magneton value but such i s certainly not the case, A cd > C o -p u o P3 1.5 1.4 1.3 1.2 1.1 1.0 p Mno0Ga2oC20 ,0 Mn6oAl2oC20 / -HD Mn60Zn2QC20 .3.850 3.875 3.900 Lattice Parameter A° 3.925 Figure 15 Variation of Bohr magneton value with l a t t i c e parameter for Mn6oAl20p20» Mn60Ga2oC20s and Mn6oZn2oC20" Perhaps a look at the Mn6oAlxZn2o_xC20 system may serve to de-emphasize even further the role of the interatomic distance i n affecting the magnetic moment. As the aluminum content i s increased from 0 to 20 percent the magnetic moment decreases, reaching a minimum at approximately 5.5 percent, and then increases. The lat t i c e parameter however decreases linearly over the same range. A f a i r l y similar state of affairs i s also found i n the Mn6oGaxZn20-xG20 system as can be seen from the graphs i n the results section. The variation of the l a t t i c e parameter with the magnetic moment as shown i n the above two systems certainly appears to point to the fact that interatomic distance i s not a governing factor i n the alloy systems under discussion. - 40 - Returning once again to the variation of Bohr magneton value with atomic percent aluminum i n the Mn 0 oAl xZn2o« x^20 system we note that the type of variation obtained (namely a decrease and then a increase i n the Bohr magneton value) would seem to further rule out any simple valency mechanism. If a simple valency mechanism were operative we would expect a linear decrease in the Bohr magneton value when going from Mn6oZn2oG2o to Mn 0oAl2oC20 4 E v e n though single phase alloys are not available i n the Mn0QGaxZn2o-x^20 beyond 6.63 percent gallium i t may be inferred from the results that the Bohr magneton value decreases with increasing gallium content up to 5.75 percent and then i t should increase i n some manner u n t i l i t reaches the value expected for M^oC^O^O0 Once again we may conclude that a simple valency mechanism i s not operative. Intensity plots made with X-ray goniometer at 20°C and -1B6°C for an alloy of 2.85 atomic percent aluminum i n the Mn^QAl xZn2o_ x^20 system indicates that the original facescentered cubic structure observed at room temperature i s sl i g h t l y distorted becoming face-centered tetragonal at -186°C. This is similar to the transition mentioned earlier for an alloy near the composition Mn0QZn2QC2Q i n which case i t was also noted that the transition i n structure corresponded to a maximum i n the saturation magnetization versus temperature curve. It therefore seems jus t i f i a b l e i n assuming that, for alloys i n the Mn£)oAlxZn2o-xC2o a n d M n 6 0 G a x Z n 2 0~x^ 2 0 systems i n which a maximum i n the saturation magnetization occurs, a trans i  tion i n structure occurs at a temperature corresponding to that at which the maximum appears. However, the maximum i n the saturation magnetization curve i s not considered to be due to the transition i n structure. In fact, i f we - 41 - use the concept outlined earlier for the Mn-Zn-C system, whereby we have two opposing sublattices having different Curie points i . e . an ordering of manganese atoms, then i t appears that the transition i n structure i s due to ordering of manganese atoms which occurs at a temperature corres ponding to the maximum i n the saturation magnetization curve. No attempt w i l l be made to try and explain the unexpected type of variation of Bohr magneton value with atomic percent aluminum or gallium i n the Mn6oA^xZn20-x<'20 o r ^ 160 G ax Z n20-xO20 systems. Similarly the mechanism operative i n causing maximum i n saturation magnetization curves w i l l not be discussed further. We shal l note that the magnetic anomaly appears to dissappear near an aluminum content of 5.5 atomic percent i n Mn60AlxZn2Q_xC2o system and near a gallium content of 5.75 atomic percent i n Mn6QGaxZn20-xC20 system. Considering the transition temperatures i n the alloys possessing an anomaly i n saturation magnetization plot, i t is found that the transition temperature decreases with increasing aluminum or gallium thus indicating that i t requires a lower temperature for ordering of the manganese atoms to occur. It i s f e l t that in order to try and explain magnetic properties Of above systems that one would have to take into account such items as tot a l number of electrons and exchange forces between these electrons. Such a study would be rather d i f f i c u l t and i s beyond the scope of this investigation. - 42 - VI. BIBLIOGRAPHY 1. F. Brailsford, Magnetic Materials (1951) 29. 2. R.G. Butters, H.P. Myers, Philosophical Magazine, (1955), 46, 895. 3. R.G. Butters, H.P. Myers, Philosophical Magazine, (1955), 46, 132. 4. L. Neel, Annales de Physique, (1948), 3, 137. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0081196/manifest

Comment

Related Items